Will tonight's sky be worth it?

The live score is meant to answer one simple question: is tonight worth going out for? It combines the weather, the moon, local light pollution and the length of the dark window into one 0 to 10 score.

• Cloud cover carries the most weight. We score the forecast during the dark hours, not just the weather at the moment you open the page.
• Light pollution comes from the viewing-spot picker. A city centre hides most faint stars, while a dark-sky site gives you a much better chance of seeing the Milky Way.
• Moonlight is based on the moon phase calculated in your browser. A bright moon lowers the score, unless it has already set by the time the sky is dark.
• Dark hours measure how long the sky stays properly dark after twilight. When you are online we use tonight's twilight times. If those are unavailable, we estimate the window from your latitude and the date.

The parks table compares places where night-sky quality is part of the visitor experience. The score favours dark skies first, then gives extra weight to places that are more likely to have clear nights.

• Certified status means the park or NPS unit appears in DarkSky International's certified-places programme, or is matched against NPS night-sky material. We only treat the certification year as verified when we can trace it to those sources.
• Bortle value is an estimate where the park does not publish a measured figure. We use certification level, published sky-quality descriptions and light-pollution context to keep the comparison consistent.
• Clear nights are estimated from regional climate patterns where park-level clear-night data is not available.
• Confidence level is why the default table starts with the highest-confidence certified set. The additional-parks view is useful for inspiration, but some of those rows still need stronger source confirmation.
• CSV download keeps the full set of values in one place, including which rows are estimated.

Sources. DarkSky International certified-places registry, NPS Night Skies program, Open-Meteo for the forecast, sunrise-sunset.org for twilight times, and Sky & Telescope for the Bortle dark-sky scale.

The towns table is for trip planning. It does not claim the middle of town is the darkest place to stand. It asks a more practical question: which towns make good bases for a stargazing break?

• Sky Darkness Score reflects nearby dark-sky designations, protected landscapes, observatory regions and local light-pollution context. Towns score better when darker skies are close by.
• Average Cloud Cover uses longer-run cloud data for the area, not tonight's forecast. A dark place drops down the table if cloudy nights are common.
• Nearby Dark-Sky Area names the main viewing area or landscape that makes the town useful as a base.
• Trip Ease Score covers the practical side of a visit, including places to stay, eat, refuel and start a night-sky drive from.
• Elevation is a supporting factor because higher ground can mean clearer, drier air. It helps, but it does not outweigh darkness or clouds.
• Country split keeps US and UK towns separate because the climate, road distances and access to dark-sky landscapes are so different.

Sources. Dark-sky status and recognised viewing areas are checked against DarkSky International Places, CPRE dark skies resources and local park or observatory information. Cloud and elevation inputs use public climatology and mapping sources, including NASA POWER and national elevation data where available.